
function x=Derivation(Original,location,error)
    spacing = 0.001;
    tmp = error + 1;
    a = 0;   b = 0;
    while(tmp > error)
        a = (Original(location + spacing) - Original(location) ) / spacing;
        b = (Original(location) - Original(location - spacing) ) / spacing;
        tmp = abs(a-b); 
        spacing = spacing/2;
    end
    x = (a + b) / 2;
end